This invention relates generally to an automatic identification of a transponder on an object responsive to a signal from a remote interrogating station, and more particularly to an improved transponder.
Transponders of the type disclosed herein can be mounted on vehicles, and in response to an interrogating signal from a remote interrogator, transmit information previously recorded and stored in the transponder relating to vehicular identification and/or other data necessary for management and operational control of vehicles such as trucks, buses, or rail vehicles operating on rails, including freight, locomotive, and mass transit passenger cars. Some applications, however, utilize a moving interrogator mounted on the vehicle and a stationary transponder in order to establish position or location of the vehicle and/or to transmit other information to operators of the vehicle.
Presently, known vehicular identification systems employ a transponder such as disclosed in U.S. Pat. No. 3,918,057, for use in a system disclosed and claimed in U.S. Pat. No. 4,068,211. The specification and figures of U.S. Pat. No. 4,068,211 is hereby incorporated by reference. The system and transponder disclosed herein utilize the well known frequency shift keying (FSK) method wherein carriers of two frequencies are modulated or shifted in bit format to contain information stored in the transponder for transmission from a moving transponder to a fixed location interrogator. This information is encoded through a transmitted string of digital non-return to zero (NRZ) bits coded by shifts from one frequency to another over a fixed time period. These presently used devices utilize conventional or Colpits or Hartley oscillators to generate the dual frequencies required from FSK signaling.
Although this type of transponder is in use generally speaking, operational difficulties have been encountered, primarily with the frequency generating means due to frequency stability, sensitivity to the proximity of ferrous materials and temperature sensitively of the frequency generating oscillators.
The transponder of this invention overcomes these objections and provides further advantages through the use of a programmed microprocessor.
Therefore, it is an object of this invention to provide a frequency shift keyed (FSK) transponder for use with existing interrogators having improved frequency stability through incorporation of a microprocessor having a highly accurate internal crystal controlled frequency.
It is an additional object of this invention to provide an improved FSK transponder wherein microprocessor programming precisely controls the generation of frequency shift keyed signals for transmission to a remote interrogator.
It is an additional object of this invention to provide a frequency shift keyed transponder utilizing microprocessor programming to insure accurate transmission of stored information through verification of the content of each information bit transmitted on each transmission cycle.
It is a further object of this invention to provide a frequency shift keyed transponder wherein shift frequencies, stored information, and handling of other data can be conveniently modified and/or improved through microprocessor programming.